<template>
	<ul class="list">
		<li 
		class="item" 
		v-for="item in letters" 
		:key="item" 
		:ref="item"
		@click="handleLetterClick"
		@touchstart="handleTouchStart"
		@touchmove="handleTouchMove"
		@touchend="handleTouchEnd">{{item}}</li>
	</ul>
</template>

<script>
	export default{
		props:{
			cities:Object
		},
		data(){
			return{
				touchStatus:false,
				timer:null
			}
		},
		computed:{
			letters(){
				const letters=[]
				for(let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		methods:{
			handleLetterClick(e){
				this.$emit('change',e.target.innerText)
			},
			handleTouchStart(){
				this.touchStatus=true
			},
			handleTouchMove(e){
				if(this.touchStatus){
					if(this.timer){
						clearTimeout(this.timer)
					}
					this.timer=setTimeout(()=>{			//js 函数节流
						const startY=this.$refs['A'][0].offsetTop
						const touchY=e.touches[0].clientY-79
						const index=Math.floor((touchY-startY)/20)
						if(index>=0&&index<this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)
					
				}
			},
			handleTouchEnd(){
				this.touchStatus=false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import "~styles/varibles.styl"
	.list
		display flex
		flex-direction column
		justify-content center
		position absolute
		top 1.58rem
		right 0
		bottom 0
		width .4rem
		.item
			line-height .4rem
			text-align center
			color $bgColor
</style>